This invention relates to packing machines, particularly to thermal insulation packing machines and to the use of such packing machines to pack pre-compressed rolls of thermal insulation.
Thermal insulation such as glass fibre or rock wool is produced in the form of a continuous mat or web which is cut to lengths and may be compression rolled on a machine such as that described in European Patent No. 131475. That machine ensures that the compressed roll is prevented from unwinding by applying a sheet of paper around the curved surface of the cylinder. To prevent loss of fibres or damage to the roll so formed, it is usual to wrap this compressed cylinder in polythene. To do this the roll is transferred to a packing machine which first aligns the roll with the web from a large roll of polythene and then leads the edge of the polythene around the roll of insulation. Nominally only one length of insulation cylinder can be wrapped by such a machine, which leads to the need to have multiple machines when production needs to be switched from one type of insulation product to another having a different length. Furthermore, the exposed ends of the polythene need to be clipped to seal the package and in the known process this clipping operation requires the excess polythene to be gathered by rotating the entire roll and package slowly passed gathering brushes and then applying the clips simultaneously to each end of the pack. The main drawbacks of this system are that the process is slow. Also it is not easy to get the polythene to wrap tightly about the insulation roll, which gives rise to ballooning of the package. This is both unsightly and costly because it could entail the product taking up more room during storage and transport. The slow speed of operation means that several such machines have to be used to take the output of a single compression rolling machine and this is expensive and wastes valuable floor space.
Insulation packing machines are also known in which the polythene wrapping material is welded into a continuous tube longitudinally around the insulating material. Such a machine is described in CB patent application No. 2125760A which is primarily for wrapping stacks of insulation in slab form. The machine compresses the slabs between two conveyors which feed the compressed insulation into a welded plastic tube. The tube is formed from a special double folded roll of polythene. Because the insulation will ultimately be held in compression by the polythene tube itself, it is necessary to allow the longitudinal heat weld to cool and strengthen before the conveyors can actually deliver the insulation into a free-standing tube of plastic. This makes the process cycle time excessively long. In one version of this machine, transverse heat welds are made between the stacks of insulation slabs. To make such welds the polythene must be gathered between two bars and to prevent overstretching of the polythene during this gathering, the insulation pack that is already inside the tube with its remote end sealed, must be free to move backwards. Thus, the excess tube length is created in the void between the two stacks of insulation slabs by removing the half sealed pack to a larger distance than is required for it to clear the transverse heat welding equipment and then allowing it to move back nearer to that minimum clearance. This extra movement slows the process considerably because the half sealed pack can only be removed at the rate that continuous tube can be formed by the longitudinal welding around the compression conveyors, and whilst in principle more heat could be applied, this would in practice cause overheating and increase the time that the weld would have to be allowed to cool before the process cycle could continue. A further disadvantage of this process is that air is trapped in the tube area between the two stacks of slabs and tends to be compressed when the volume is reduced by application of the gathering bars and backward motion of the half sealed pack. This air causes ballooning of the pack which is then partially eliminated when the pack and contents are removed from the effect of compression due to the conveyors above and below the pack. It will be appreciated that such over-compression is undesirable because it damages the insulation, particularly if it is glass fibre insulation. Furthermore, it is difficult to apply such compression to a roll which is sheathed in paper.